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Wind energy innovators have long dreamed of harvesting wind energy from rooftops, but the going has been slow in terms of mass market adoption. That could be about to change. A US startup has come up with a business model that leverages solar industry know-how to help cut the cost of rooftop wind turbine installations, and it has caught the eye of the US Department of Energy.
The Small Wind Turbine Challenge
Rooftops or not, developing an economical way to harvest energy from slower wind speeds is the main challenge of the small wind turbine field. Instead of tall towers and massive blades that can reach optimal wind speeds far off the ground, small wind turbines have to make the most of whatever wind is available closer to the ground.
Proximity to the ground also constrains the size of the blades, layering on another engineering challenge.
Here in the US, the small wind turbine industry was hampered by a lack of standards and transparency in the early 2000’s, until the Energy Department’s National Renewable Energy Laboratory in Colorado stepped in to launch a small wind testing program. That was followed by the establishment of the Small Wind Certification Council in 2008.
Small Wind Turbines Everywhere
Stimulating growth in the small wind turbine industry is still a challenge, though. Compared to the skyrocketing appeal of rooftop solar and other small-sized solar arrays, small-scale wind has been a tough sell.
The Energy Department has been focusing its small wind efforts on rural or semi-rural applications, where small wind turbines can be mounted on towers. In its 2023 wind markets report, the Energy Department noted that agriculture is currently driving growth in the small wind industry.
The Energy Department is also determined to pitch small wind for household use. “If you have enough wind resource in your area and the situation is right, small wind electric systems are one of the most cost-effective home-based renewable energy systems — with zero emissions and pollution,” they enthuse in an online primer.
The Rooftop Wind Turbine Opportunity
Promoting small wind turbines for installation on rooftops opens up a whole other can of worms.
For starters, rooftop installation gives rise to another layer of engineering challenges, in order to prevent vibration and noise from affecting the host building.
“Also, the wind resource on the rooftop is in an area of increased turbulence, which can shorten the life of the turbine and reduce energy production,” the Energy Department has noted. “Additional costs related to mitigating these concerns, combined with the fact that they produce less power, make rooftop-mounted wind turbines less cost-effective than small wind systems that are installed on a tower connected to the ground.”
That’s the bad news. The good news is that rooftop wind turbines are just about the only way to introduce more small-scale wind power into cities, where land for turbine towers is scarce. And, since science loves a challenge, solutions are emerging.
A New Business Model For Rooftop Wind Turbines
That brings us to the US startup Accelerate Wind. The company’s CEO and founder, Erika Boeing, came up with the idea of piggybacking rooftop wind turbines with the rooftop solar industry as an effective cost-cutter, and that caught the attention of the Chain Reaction Innovations (CRI) incubator at the Energy Department’s Argonne National Laboratory in Illinois, near the windy city of Chicago.
As part of Accelerate’s residency at CRI, a prototype of the company’s rooftop wind turbine system was installed at a building on the Argonne campus, consisting of two parts: a wind-capturing airfoil that hangs over the edge of the roof, and cost-cutting improvements to the wind turbine.
The airfoil “captures and channels the wind that is naturally faster at the edge of the roof due to pressure differences between the building face and the roof,” Argonne explains. “Higher-speed wind is directed toward the turbine, allowing for a four-fold increase in power compared with installation without the airfoil.”
Among the cost-cutting wind turbine improvements described by Argonne are an on-board intermediate energy storage system and a supply chain that leverages commonly available components.
“With a novel system configuration designed to maximize wind capture and conversion, the prototype turbine could drive down wind energy costs by 60 percent or more, making rooftop wind generation a cost-effective prospect,” Argonne enthuses.
The Rooftop Solar Connection
New technology is just part of the cost-effective rooftop wind turbine equation. Just as permitting, labor, marketing, and other “soft costs” make a significant contribution to the overall expense of installing a rooftop solar array, they also factor into rooftop wind turbine projects.
In an explainer posted on the Argonne website, Boeing emphasized Accelerate’s attention to soft costs.
“Accelerate Wind is the first to really think through the cost equation of rooftop wind turbines holistically, tackling energy capture at the edge, power electronics, and the soft costs involved in sales and installation,” she said. “This solution will allow wind energy to scale in the market alongside the rooftop solar market that has significant market penetration today.”
The piggyback effect surfaces in two different ways. First, Boeing and her team designed the installation of their rooftop wind turbine system to be consistent with rooftop solar arrays, creating the potential to cross-train solar installers.
Second, the edge-of-roof placement of the airfoil and wind turbine leave plenty of room for rooftop solar arrays, enabling buildings to harvest solar energy by day while the rooftop wind turbines keep the clean kilowatts coming at night.
Completing the picture is a modular system, similar to that deployed by the rooftop solar industry, that enables building owners to right-size their wind turbine arrays.
Aiming Rooftop Wind Turbines At Commercial Buildings
Accelerate Wind has spotted an opportunity in the commercial buildings market, where rooftop solar has already taken firm hold. As Argonne notes, most commercial buildings don’t have enough rooftop space for a solar array large enough to supply all of their energy needs. Rooftop wind turbines could help fill in the blanks.
Despite the challenges, things seem to be looking up for rooftop wind turbines. Last year Accelerate was selected by the Amazon Web Services branch of Amazon to participate in its Sustainable Cities Accelerator. It was also selected for a grant from the Innovate Alabama program, and its pilot project at Argonne earned it a slot in the federal General Services Administration’s Green Proving Ground program.
The airfoil strategy adopted by Accelerate also shares some characteristics with ducted wind turbines, which deploy a sort of hood or shroud to steer more wind energy into the blades. Activity seems to be stirring in that area as well.
In addition, the Inflation Reduction Act could provide some much-needed incentives to help push small wind turbines out of the marketing doldrums, so stay tuned for more on that.
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Photo: An innovative new rooftop wind turbine leverages an airfoil to capture more wind energy at low altitudes (courtesy of Argonne National Laboratory).
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